The vast majority of fuels are distilled from crude oil pumped from limited underground reserves or mined from coal. As the earth's crude oil supplies become more difficult and expensive to collect and there is growing concerns about the environmental effects of coal other than clean anthracite coal, the world-wide demand for energy is simultaneously growing. Over the next ten years, depletion of the remaining world's easily accessible crude oil reserves and clean anthracite coal reserves will lead to a significant increase in cost for fuel obtained from crude oil and coal.
The search to find processes that can efficiently convert biomass to fuels and by-products suitable for transportation and/or heating is an important factor in meeting the ever-increasing demand for energy. In addition, processes that have solid byproducts that have improved utility are also increasingly in demand.
Biomass is a renewable organic-carbon-containing feedstock that contains plant cells and has shown promise as an economical sourced of fuel. However, this feedstock typically contains too much water and contaminants such as water-soluble salts to make it an economical alternative to common sources of fuel such as coal, petroleum, or natural gas.
Historically, through traditional mechanical/chemical processes, plants would give up a little less than 25 weight percent of their moisture. And, even if the plants were sun or kiln-dried, the natural and man-made chemicals and water-soluble salts that remain in the plant cells combine to create corrosion and disruptive glazes in furnaces. Also, the remaining moisture lowers the heat-producing MMBTU per ton energy density of the feedstock thus limiting a furnace's efficiency. Centuries of data obtained through experimentation with a multitude of biomass materials all support the conclusion that increasingly larger increments of energy are required to achieve increasingly smaller increments of bulk density improvement. Thus, municipal waste facilities that process organic-carbon-containing feedstock, a broader class of feedstock that includes materials that contain plant cells, generally operate in an energy deficient manner that costs municipalities money. Similarly, the energy needed to process agricultural waste, also included under the general term of organic-carbon-containing feedstock, for the waste to be an effective substitute for coal or petroleum are not commercial without some sort of governmental subsidies and generally contain unsatisfactory levels of either or both water or water-soluble salts. The cost to suitably prepare such feedstock in a large enough volume to be commercially successful is expensive and currently uneconomical. Also, the suitable plant-cell-containing feedstock that is available in sufficient volume to be commercially useful generally has water-soluble salt contents that result in adverse fouling and contamination scenarios with conventional processes. Suitable land for growing a sufficient amount of energy crops to make economic sense typically are found in locations that result in high water-soluble salt content in the plant cells, i.e., often over 4000 mg/kg on a dry basis.
Efforts to make a synthetic liquid fuel called pyrolysis oil, also known as biocrude or biooil, from organic-carbon-containing feedstock have been tried as a substitute for petroleum. Present methods of making pyrolysis oil have not resulted in a satisfactory liquid feedstock for petroleum refineries. The efforts to date have not been economically viable as the processed feedstock generally contain unsatisfactory amounts of water-soluble salts that can contribute to corrosion, fouling, and slagging in combustion equipment, and have high water content that reduces the energy density to well below that of petroleum in large part because of the retained moisture. However, there remains a need for processed pyrolysis oil as a clean renewable source of liquid fuel if it could be made cost-effectively with a more substantial reduction in its content of water and water-soluble salt.